The chlorination of nitrobenzene produces an isomeric mixture containing the meta isomer as the major chloronitrobenzene constituent. It is believed that other methods of producing chloronitrobenzene, such as the nitration of chlorobenzene, produce products in which the distribution of the ortho, meta, and para isomers differ from that obtained by the chlorination of nitrobenzene.
The separation of mixtures of chloronitrobenzene isomers, into pure or substantially pure fractions is known to present problems in that many of the precedures are yield limited and/or involve a series of complex process steps. There is interest by the chemical industry in economically obtaining the meta isomer of chloronitrobenzene in substantially pure form for use as a chemical intermediate in various processes. The simple high yield process disclosed herein for accomplishing that object is of particular interest for that reason.
Among the procedures for separating mixtures of chloronitrobenzene isomers described in the art are the following:
U.S. Pat. No. 3,311,666, to Dunn, relates to the separation of chloronitrobenzene isomers by crystallization and fractionation and discusses the difficulties encountered in distillation and crystallization techniques.
U.S. Pat. No. 3,816,551, to Lee, relates to the use of crystallization in separating isomers of chloronitrobenzene. Specifically, the para isomer is separated employing continuous crystallization in the presence of water.
U.S. Pat. No. 2,795,620 and U.S. Pat. No. 2,795,621 to Bloom et al, discuss various methods for the manufacture of meta-chloronitrobenzene and problems related to chloronitrobenzene isomer separation. The patents are specifically directed to separating ortho- and para-chloronitrobenzene from meta-chloronitrobenzene by means of a sulfonation Process.
U.S. Pat.No. 2,245,945, to van Dijck et al, relates to a process for the separation of isomeric organic compounds, including mixtures of ortho- and para-chloronitrobenzene, by the use of two selective solvents partially immiscible with one another to cause distribution of the isomers between the solvents.
U.S. Pat. No. 3,051,650, to Pfennig relates to separating chemical compounds using solvents and liquified sulfur dioxide.